It has been recently discovered that zirconium chlorohydrides having the formula ##STR3## WHEREIN R is an unsubstituted .pi.-cyclopentadienyl radical are attractively useful in terminally functionalizing either internal or terminal olefins. In accordance with such utility, reaction of the chlorohydride with the olefin under mild conditions (e.g. 25.degree.-40.degree. C. in benzene) rapidly produces an alkylzirconium complex, the alkyl moiety of which is 1-substituted and the zirconium moiety of which can be readily replaced with a desired functional group, e.g. by cleaving the complex with an electrophilic reagent such as Br.sub.2, I.sub.2 or C.sub.6 H.sub.6 ICl.sub.2 to prepare a terminally halogenated alkane or by first inserting a CO radical into the C--Zr bond of the complex and then cleaving the complex with a similar electrophilic reagent to prepare an alkane having a terminal acylhalide substituent. Illustrations of such uses of a di(.pi.-cyclopentadienyl) zirconium chlorohydride have been published by J. Schwartz and other in J. Amer. Chem. Soc. at 96, 8115-16 (1974) and 97, 228-30 and 679-80 (1975) and in Angew. Chem. Int. Ed. Engl. at 15, No. 6, 333-40 (1976).
From those published illustrations it is apparent that the di(.pi.-cyclopentadienyl) chlorozirconium moiety cleaved from the alkylzirconium complex by use of such an electrophilic group is concurrently further halogenated, producing a corresponding dihalide, and that one mole of the zirconium chlorohydride is converted to such a dihalide for each mole of olefin that is terminally functionalized. Thus the economic attractiveness of the olefin terminalizing process is highly dependent on the availability of a convenient procedure for converting the zirconium dihalide back to the chlorohydride which may be recycled for use in terminalizing more of the olefin.
Preparations of chlorohydrides of this kind from the corresponding dihalides have been previously described. For example, in J. Organometal. Chem., 24, 405-11 (1970), P. C. Wailes and H. Weigold describe the preparation of a di(.pi.-cyclopentadienyl) zirconium chlorohydride by treatment of the corresponding dichloride with a stoichiometric amount of an alkali metal aluminum hydride which may be LiAlH.sub.4 or LiAlH-(O-t-butyl).sub.3, and in J. Amer. Chem. Soc., 96, 8115-16 (1974), O. W. Hart and J. Schwartz describe carrying out the same reaction by treating the dihalide with Vitride, i.e. a solution of NaAlH.sub.2 (OCH.sub.2 CH.sub.2 OCH.sub.3).sub.2 in benzene. A preparation of the same chlorohydride by treatment of the dichloride with metallic magnesium in tetrahydrofuran is also described in the aforementioned article by Wailes and Weigold. Each of those procedures, however, has serious drawbacks for commercial application. For instance, the alkali metal aluminum hydrides used as just mentioned are very expensive and, as described in the article by Wailes and Weigold, the yield of the procedure carried out with metallic magnesium is quite low (on the order of 30 %).
Other attempts to convert such a dichloride to the corresponding chlorohydride have been completely unsuccessful. For instance, an uncatalyzed contacting of the same dichloride with molecular hydrogen under elevated pressure at 25.degree. C. produced no discernible reaction, and the addition of a well-known homogeneous hydrogenation catalyst (tris-triphenylphosphine rhodium chloride) to the mixture likewise resulted in no detectable reaction.
It will be clear from the foregoing that a process by which the aforementioned and similar zirconium halohydrides can be more attractively produced from the corresponding dihalides is very desirable, and it is an object of this invention to provide such a process. Further objects of this invention will be apparent from the following disclosure in which all percentages are by weight except where otherwise noted.